1. Technical Field
The invention relates generally to underwater cable fairings, and in particular to a protective fairing for an underwater sensor line array.
2. Background Art
U.S. Pat. No. 3,343,516, which issued on Sep. 26, 1967, to D. A. Nichols et al, describes a towline for the towing of a submerged object, such as a sonar device, from a ship. The towline includes a flexible strength member, e.g., a steel wire rope, carrying a plurality of streamlined fairing sections and a stretchable electrical cable passing through the fairing sections and extending along the strength member to the sonar device. The ship has a rotatable drum upon which the towline is wound for storage. The fairing sections prevents vibration of the strength member as the sonar device is towed at various speeds and provides protection, both in the water and on the ship, for the electrical cable.
U.S. Pat. No. 3,304,364, which issued on Feb. 14, 1967, to A. C. Hetherington, describes a towline for towing a submerged object, such as a sonar device, behind a parent towing vessel, one end of the towline being connected to the submerged object and the other end being secured to the parent towing vessel by a take-up winding drum. The towline includes an elongated body portion of resilient material having an outer transverse cross section which is streamlined in general appearance to prevent lateral whipping of the towline and to provide minimum drag and insure depth control. The resilient body portion houses a continuous non-stretchable tension member, such as a steel wire rope, as well as a continuous assembly of yieldable electrical conductors.
U.S. Pat. No. 3,859,949, which issued on Jan. 14, 1975, to Toussaint et al, describes jacketing for underwater cables and drag ropes, with streamline profile, comprising two completely separable profiled strips for individual reeling, the two strips being snapped together, with joints only at the leading and trailing edges of the profile. Each strip has a recess which mutually cover each other upon assembly and define an elongated cavity for loosely receiving the rope or cable. The two strips may also define limited space cavities for receiving pieces of equipment, such as measuring transducers.
A common technique for constructing an undersea hydrophone line array is to attach a series of hydrophones to the side of a specially designed electromechanical cable. The electromechanical cable is typically composed of a central core of individually insulated electrical conductors which are over-braided with KEVLAR fibers for strength and DACRON fibers for abrasion resistance. The individual conductors to be connected to a particular hydrophone are cut, the ends of these conductors extracted through the outer covering at the desired location for that hydrophone, and waterproof electrical connectors applied to the conductor ends as necessary for mating with the hydrophones. A protective housing for the hydrophone is affixed to the outer surface of the electromechanical cable by any of various connection devices such as clamps, cords or tape for underwater use. The hydrophone is inserted into its protective housing, the electrical connectors are mated, and any excess wiring to the hydrophone secured within the protective housing.
Typically, the hydrophone line array may be one hundred meters or more in length, and may include a hundred or more hydrophones and several other sensors, e.g., tilt, magnetic heading, and pressure sensors, which are connected to respective conductors of the electromechanical cable in the same manner as described above. In many applications, the hydrophone line array is connected to the surface ship by a long cable having a length of one thousand meters or more, so that the hydrophone line array can be deployed in very deep water. For this reason, the electromechanical cable usually includes electrical conductors for telemeter signals and a telemeter signal generating apparatus is disposed at the lower end of the hydrophone line array, so that the signals from the hydrophones are supplied to the nearby telemeter signal generating apparatus which converts the hydrophone signals into telemeter signals for transmission to the surface ship.
In certain applications, the hydrophone array cable passes off the deck of a ship into the water with little applied tension, is detached from the ship and descends to the ocean bottom where data is collected, and is then released from its mooring and floats to the sea surface. In such applications, the array cable is recovered with little potential of damage to the cable or hydrophones due to handling. In other applications, the hydrophone array must be repeatedly lowered and raised over the side of the ship while under considerable tension. This is accomplished by driving the cable onto or off a winch and over a sheave suspended over the side of the ship. As the hydrophones in their protective housings pass over the sheave or onto the winch, they must be aligned such that they are not pinched between the load-bearing cable and the rotating surface of the sheave or winch. If this is not ensured, damage to the housings, hydrophones, cable pig tails, or the electromechanical cable may result. For example, in the past, the hydrophone protective housings have been crushed and ripped from their fastenings to the electromechanical cable, and the unprotected conductor leads have been pinched and cut, causing water intrusion. When such damage occurs in a line array having many hydrophones or other sensors, e.g., eighty or ninety, the repair of such damage can be very costly and time-consuming.